Download Hawaiian Slumps

Shield volcanoes, built almost entirely of lava flows, occur at mid-ocean
ridges and hot spots. They have gentle topographic profiles and the lava
is fluid. Lava fountains and flows may be spectacular. The Hawaiian
shield volcanoes threaten sensitive coastal ecosystems, transportation
and communication networks, and populated regions. Volcanic emissions
are of interest to scientists who study the atmosphere. Underwater
volcanoes heat the ocean and change the sea floor topography. These
changes can cause the global sea level to rise and affect weather patterns.
Tsunamis caused by debris avalanches pose a threat to the Hawaiian
coast. Earth-observing satellites, such as NOAA's Geostationary
Operational Environmental Satellites (GOES), gather and relay valuable
data which are crucial in efforts to minimize losses from hazardous
volcanic activity.
Stratovolcanoes (also known as composite volcanoes) are built of
successive layers of ash and lava. The magma (molten rock) within the
volcano is viscous and often contains trapped gas, causing explosive
eruptions. The clouds of ash from the volcanic eruptions present a hazard
to aviation. We use imagery from polar orbiting and geostationary
satellites to detect the boundaries of a volcanic ash cloud, and estimates
the altitude and movement of the ash plume. NOAA distributes Volcanic
Ash Advisory Statements (VAAS) to warn aircraft pilots of hazardous
ash clouds. Particles erupted into the stratosphere during major eruptions
can change global temperature by several degrees, altering weather
patterns and effecting global agriculture.
Approximately 85% of stratovolcanoes are located around the Pacific
Ocean, forming what is called the "Ring of Fire."
Stratovolcanoes occur at the margins of tectonic plates, large sections of
Earth's crust that move together. The continental plates, composed of less
dense material, override the oceanic plates. Magma generated from the
subducting plate rises and squeezes into cracks, eventually reaching the
surface in a volcanic eruption.
RECORD RIDE: Pete Cabrinha, off Maui, Hawaii, in January, surfing
the 70-ft. monster that won him the 2004 Billabong XXL Award. It is
given annually to the rider of the biggest wave
Earth' s oceanic and continental crust is broken up into about ten major
plates and several minor ones. Each plate is about 100-150 kilometers
thick. They are all moving in different directions related to one another.
An abundant amount of energy is dispersed as the plates move apart,
collide, and slide by each other at the plate margins. Thus, it is at these
plate boundaries where the most momentous geologic marvels occur
such as mountain building, earthquakes, and volcanic activity.
Volcanoes are one of nature’s most awesome forces. These natural vents
and fissures erupt molten rock and gases from deep inside the earth.
Unlike most volcanoes created in plate boundaries, these volcanoes are
far from such things. Many of them, like the Hawaiian hot spot, lie in
the center of a plate. Secondly, they make up a very small fraction, less
than one percent, of all the volcanic activity in the world. Thirdly, they
produce linear island chains which have a distinctive age progression.
And lastly, lavas that are generated by the volcanoes are also unique.
They are composed of basalts and are richer in alkali metals such as
sodium, potassium, and lithium. (Abbott, Macdonald, & Peterson, 1983)
The plume hypothesis survived largely as a belief system and had to be
extensively modified to account for unexpected observations.” G. R.
Foulger and J. H. Natland, “Is ‘Hotspot’ Volcanism a Consequence of
Plate Tectonics?” Science, Vol. 300, 9 May 2003, p. 921.
“It seems that we must abandon the convenient concept of fixed hotspots
as reference points for past plate motions.” Ulrich Christensen, “Fixed
Hotspots Gone with the Wind,” Nature, Vol. 391, 19 February 1998, p.
740.
“It was later shown, however, that the Pacific hotspots move relative to
those in the Atlantic at rates of 1–2 cm yr-1. This is less than the speed of
fast-moving plates (10 cm yr-1), but enough to make the hotspot frame
of reference suspect.”
The Cook-Austral and Marquesas chains, for example, are marked by
gross violations of a simple age-distance relationship and by extreme
variations of isotopic signature, inconsistent with a single volcanic
source. The Hawaiian-Emperor chain provides a more consistent age
sequence, but there is no systematic variation of heat flow across the
Hawaiian swell, contradicting the simple hotspot model (Keith, 1993).
Plumes: hypothetical entities considered to be strong, active upwellings
in contrast to passive upwellings caused by plate divergence. Plumes are
assumed to provide magma to hotspots such as ocean islands. Plume
heads are assumed by some authors to be responsible for surface uplift,
breaking of the lithosphere and large igneous provinces (LIPs).
The modern thinking about plumes is substantially different; plumes are
considered to reflect a secondary mode of convection unrelated to (and
little affected by) plate-scale convection.
The idealized plume has two components: a plume head, supposedly
responsible for very short-lived, massive igneous events, and a narrow
plume tail which generates long-lived hotspot tracks. The source of
mantle plumes is a thermal boundary layer deep in the mantle, perhaps
the core-mantle boundary, although some have argued for a shallower
source.
The complex picture of the Earth that emerges in the plume model is
compounded by uncertainties in the number of hotspots, the depth of
origin of plumes, whether hotspots are fixed, the composition of plumes,
the amount of melting in plumes, and the relationship of plumes to
Plume hypothesis has acquired the status of an unchallengeable dogma
and an obvious fact (H.C. Seth, 1998). The popular and widespread
notion that hotspot tracks are simply the products of one or more plumes
beneath moving plates is actually far from reality. Few predictions and
requirements of the mantle plume model seem to be fulfilled in the actual
geology.
The complete plume hypothesis is untestable. The narrow plume tails, 10200 km in diameter, and extending deep into the mantle are below the
resolution of geophysical techniques and cannot be resolved by numerical
or theoretical computation. They give no signal and have no measurable
effect. The geophysical effects (bathymetry, geoid, tomography) of the
large flattened plume heads are little different from alternative models of
upper mantle structure. Large scale hot regions in the upper mantle
can be generated by a variety of mechanisms.
Hawaii should have the most readily resolvable conduit as it is situated
away from ridge systems and is supposedly the strongest plume.
Investigators “searched for low-velocity anomalies in the lower mantle
beneat the hotspot, but found no low-velocity anomaly which correlated
with the surface expression of volcanism
Unfortunately for the hotspot model, measurements along the axis of the
Hawaiian swell suggested an increase in heat flow with distance away
from the supposed site of the plume. The swell may not be dynamically
supported, but merely represents a thick section of basalt” or of
“thickened peridotite predating Hawaiian volcanism. The size of the
swell does not decline along the Hawaiian chain, and there is no
corresponding swell associated with the Emperor chain. While Hawaii is
thought be the strongest currently active plume, its effects are small
compared to those expected during the mid-Cretaceous superplume event
invoked for the formation of many of the intraplate edifices on the
Pacific seafloor. Uplift associated with a Cretaceous event has been
observed, but fails to reach the amounts predicted in the plume model
The Hawaiian Islands were considered the best example of a ‘Fixed
Hotspot Plume’ phenomenon. Not explained were the large chains of
submarine volcanoes scattered over a large area next to the Hawaiian
chain, but not in line with it. One adjacent chain of volcanoes is actually
perpendicular to the Hawaiian chain. It is now recognized that if hotspots
exist, they must move.
Gravity anomalies and seafloor fabric suggest that the volume and
location of volcanism in this region is controlled by stress in the
lithosphere rather than the locus of narrow plumes rising from the deep
Earth” (V p. 479
Hawaiian landslides have been catastrophic
Volcanic activity and gentle erosion have not been the only forces to
shape the Hawaiian islands. Landslide debris has now been mapped off
of all the islands. Enormous amounts of material have traveled great
distances, indicating that the slides were truly catastrophic. The Nuuanu
and Wailau landslides, shown in the image, tore the volcanoes forming
eastern Oahu and Molokai in half, and deposited blocks large enough to
have been given names as seamounts. Tsunamis generated during these
slides would have been devastating around the entire Pacific Basin
Replacing plume theory
“There are essentially two models which have dealt with a shallow origin
for the sources of intraplate volcanism on a global scale. [One is the]
concept of an enriched `perisphere' layer residing between the
lithosphere and Mid-ocean ridge basalts (MORB)-source. The perisphere
includes the upper part of the asthenosphere and the thermal boundary
layer [at the base] of the continental mantle. The layer undergoes
continuousenrichment from subduction processes, but is essentially static
and hence encounters difficulty ingenerating long-lived volcanism as
along the Hawaiian chain” (IX p. 157). “Melts from enriched mantle are
most evident at new or slowly rifting regions, infant subduction zones,
new backarc basins, slabwindows, and mid-plate environments away
from spreading induced upwelling. Enriched mantle istherefore probably
shallow. [The perisphere] is physically isolated from the depleted mantle
not by itsstrength but by its weakness and buoyancy. It has the chemical
characteristics often attributed tocontinental lithosphere (or plume
heads)” (II p. 125). “The perisphere/asthenosphere is probably laterally
and vertically inhomogeneous” (III p. 119).
Hot areas of the upper mantle may be due to the absence of cooling
rather than the importation of plume heads from great depth in the
mantle” (III p. 108). “A moving plate, overriding a hot region of the
mantle, and being put into tension, will behave, in many respects, as if it
were being impacted from below by a giant plume head” (III p. 120).
“Hot cells are an alternative to plume heads” (III p. 120). “Rifting causes
massive magmatism if the break occurs over hot cells. CFB may result
from the upwellings of already hot, even partially molten, mantle” (III
p.99
Geologists have long assumed that the Hawaiian Islands owe their existence to a "hotspot" –
stationary plumes of magma that rise from the Earth's mantle to form Mauna Loa, Kilauea
and Hawaii's other massive volcanoes
According to conventional views, the North-South age progression of this chain indicates that the
Pacific plate has moved northward over a fixed hotspot that is currently spewing out Hawaii.
The motion of the plate shifted to the northwest ~43 mya as indicated by the bend in the
chain.
Ppaleomagnetic data (2003) suggest it really was the "hotspot" that moved south as the Emperor
chain was being formed.
1. When a rock forms, atoms of potassium start decaying into argon at a constant rate, regardless
of changes in the rock's temperature, chemistry or pressure. By measuring the number of
potassium-derived argon atoms in the samples, researchers were able to estimate that the
submerged volcanoes formed some 47 million to 81 million years ago.
2. The magnetite behaves like miniature compass needles: The closer they are to the Earth's
magnetic pole, the steeper their position. Researchers were able to verify the latitudes at
which the seamounts formed by determining the angles at which the magnetite had frozen
3. Using these data, the research team concluded that the "fixed" Hawaiian hotspot probably
crept southward between 81 million and 47 million years ago at a rate of about 44 millimeters
a year, "changing our understanding of terrestrial dynamics.
4. Given the central role the Hawaiian-Emperor bend has played as an example of [tectonic]
plate motion change, these observations now question whether major plates can undergo large
changes in direction rapidly, and whether plate boundary forces alone can play a dominant
role in controlling plate motions. These data sets indicate a much more active role of mantle
convection in controlling the distribution of volcanic islands
Tarduno et al (Science, 2003) in journal Science disputes that longstanding paradigm by concluding that the fixed hotspot in the Pacific was
not stationary after all .
research suggests that the Hawaiian hotspot actually drifted southward
between 47 and 81 million years ago during the Late Cretaceous to Early
Tertiary
This study raises fundamental questions about how the mantle works and
how plates work .
What's really going on here?
Why do these hotspots drift, and why do they suddenly stop?
We know that the mantle moves, now we have to find out how deep the
motion goes
Fujiyama in Japan. An extraordinary lenticular altocumulus cloud (cloudcap) hovers like a
spacecraft over a stratovolcano
Fragments of limu o Pele and Pele's hair, formed from lava bubbles during eruption.
Photo © 2001 MBARI
Debris from Giant Slumps or landslides off Oahu and Molokai extends
hundreds of kilometers offshore
Large landslides don't just fall to the base of the mountain
the way small ones do; they often go great distances,
some up to 30 times the distance they fell. Well known on a small
scale as a Bingham Fluid, Melosh suggests that fluidization at the base
of large landslides reduces friction to near zero (acoustic fluidization).
Slope failure on Kilauea's Submarine south flank
Offshore observations along the submarine south flank of Kilauea
volcano have revealed the subsurface structure of active submarine slope
failure and the remnants of an ancient landslide. New multichannel
reflection data and high-resolution bathymetry provide this evidence, and
suggest a dynamic interplay among slope failure, regrowth, and volcanic
spreading. Disrupted strata along the upper reaches of Kilauea's flank
denote a coherent slump, correlated with the active Hilina fault zone on
land. The slump comprises mostly slope sediments, underlain by a
detachment 3-5 km deep. Extension and subsidence along the upper
flank is compensated by uplift and folding of the slump toe, which
surfaces about midway down the submarine flank.
Reference: J.K. Morgan, G.F. Moore, and D.A. Clague (2003) Slope
failure and volcanic spreading along the submarine south flank of
Kilauea volcano, Hawaii, Journal of Geophysical Research, 108(B9):
2415. [Abstract] [Article]
Spreading of Mauna Loa's flank
MAUNA LOA - A transect of four ROV Tiburon dives across the submarine west flank of Mauna
Loa volcano yields compelling evidence for volcanic spreading and associated hydrothermal
circulation during volcano growth. A frontal bench at the toe of the flank, formerly thought to be
a downdropped block of Mauna Loa, contains a mix of volcaniclastic lithologies, including
distally derived siltstone, mudstone, and hyaloclastite. The bench is overlain by bedded gravels
and subaerially erupted pillow flows derived from local shoreline-crossing lava flows. The
volcaniclastic strata in the bench were offscraped, uplifted, and accreted to the edge of the flank,
as it plowed seaward into the surrounding moat. The accreted strata underwent significant
diagenesis, through deep burial and circulation of hydrothermal fluids expelled from porous
sediments beneath the volcano. Timing constraints for bench growth and breakup suggest that
catastrophic failure of the subaerial edifice ca. 250–200 ka triggered volcanic spreading by
reducing stresses resisting basal sliding and rift-zone inflation. Increased eruptive activity, and
westward migration of Mauna Loa's southwest rift zone, gradually rebuilt the massive flank,
arresting slip prior to detachment of the Alika 2 debris avalanche ca. 120 ka.
Reference: J.K. Morgan and D.A. Clague (2003) Volcanic spreading on Mauna Loa volcano,
Hawaii: Evidence from accretion, alteration, and exhumation of volcaniclastic sediments.
Geology: Vol. 31, No. 5, pp. 411–414. [Abstract] [Article
Conditions for landslides and canyon formation
MOLOKAI - The main break-in-slope on the northern submarine flank of Molokai at 1500 to
1250m depth is a shoreline feature that has been slightly modified by the Wailau landslide.
Submarine canyons above the break-in-slope were subaerially carved. Where such canyons cross
the break-in-slope, plunge pools may form by erosion from bedload carried down the canyons.
West Molokai Volcano's continued infrequent eruptions formed a series of small coastal sea cliffs,
now submerged, as the island subsided. Lavas exposed at the break-in-slope are subaerially
erupted and emplaced tholeiitic shield lavas. Submarine rejuvenated-stage volcanic cones formed
after the landslide took place and following at least 400-500m of subsidence after the main breakin-slope had formed. The sea cliff on east Molokai is not the headwall of the landslide, nor did it
form entirely by erosion. It may mark the location of a listric fault similar to the Hilina faults on
present-day Kilauea Volcano. The Wailau landslide occurred about 1.5 Ma and the Kalaupapa
Peninsula most likely formed 330 +5ka. At their peak, West and East Molokai stood 1.6 and 3 km
above sea level.
High rainfall causes high surface runoff and formation of canyons, and increases groundwater
pressure that during dike intrusions may lead to flank failure. Active shield or postshield
volcanism (with dikes injected along rift zones) and high rainfall appear to be two components
needed to trigger the deep-seated giant Hawaiian landslides.
Reference: D.A. Clague and J.G. Moore (2002) The proximal part of the giant submarine Wailau
landslide, Molokai, Hawaii, Journal of Volcanology and Geothermal Research, 113: 259-287.
[Article]
Improvements in mapping landslides
OAHU, MOLOKAI - The development of ideas on the giant Hawaiian landslides parallels
improvements in the technology of bathymetric mapping and navigation. The landslides were
first recognized in the 1960s in a relatively detailed U.S. Navy single-beam sonar survey utilizing
an improved radio navigation system. The GLORIA multibeam side-scan sonar system (1980s)
imaged unprecedented detail in the known landslides and revealed numerous other undiscovered
ones. The JAMSTEC multibeam surveys (late 1990s), utilizing GPS navigation, produced
detailed maps of the entire landslide area for the first time.
Reference: J.G. Moore and D.A. Clague (2002) Mapping the Nuuanu and Wailau landslides in
Hawaii, In: Hawaiian Volcanoes: Deep Underwater Perspectives, E. Takahashi, P.W. Lipman,
M.O. Garcia, J. Naka, and S. Aramaki (eds), Geophysical Monograph 128, American
Geophysical Union, 223-244.
Volcaniclastic rocks on the flanks of landslide blocks
Volcaniclastic rocks on the flanks of landslide blocks
OAHU, MOLOKAI - The rocks exposed on the steep slopes of giant landslide blocks in the
Nuuanu and Wailau landslides are fragmental rocks: hyaloclastite and volcaniclastic breccias.
They form as 1) secondary slope mantling of unlithified breccia consisting of clasts in a mud
matrix; 2) hyaloclastite and breccia, all with zeolite cement, that form downslope of the shoreline
where lava flows enter the sea and fragment; and 3) breccia formed by tectonic fragmentation of
glassy submarine-erupted pillow basalt. Lavas erupted from single volcanoes are highly variable
in mayor-element composition, even during their tholeiitic shield stage, making it difficult to
identify which landslide block was derived from which volcano. Low-temperature fluids circulate
through the fragmental deposits on the flanks of the volcanoes, partially altering the glass to
palagonite and cementing the volcaniclastic rocks with Na- and K-rich zeolites. Spreading of the
volcano early in its history along low-angle thrust faults laterally transports deep submarine
pillow lava into the flank of the volcano where it crops out as tectonic breccia. The faults
underlying the landslide blocks are within this tectonized core of the volcano, not simply within
the shallow slope deposits of hyaloclastite and breccia. The Nuuanu landslide predates the 1.5 Ma
Wailau landslide.
Reference: D.A. Clague, J.G. Moore, and A.S. Davis (2002) Volcanic breccia and hyaloclastite in
blocks from the Nuuanu and Wailau landslides, Hawaii, In: Hawaiian Volcanoes: Deep
Underwater Perspectives, E. Takahashi, P.W. Lipman, M.O. Garcia, J. Naka, and S. Aramaki
(eds), Geophysical Monograph 128, American Geophysical Union, 279-296.
Uplift of strata forming Papa'u seamount and offset of surface features
along the western boundary of Kilauea indicate that the slump has been
displaced ~3km in a south-southeast direction. This trajectory matches
coseismic and continuous ground displacements for the Hilina slump
block on land, and contrasts with the southeast vergence of t he rest of
the creeping south flank. To the northeast, slope sediments are thinned
and disrupted within a recessed region of the central flank due to
catastrophic slope failure in the recent past. Debris from the collapsed
flank was shed into the moat in front of Kilauea, building an extensive
apron. Seaward sliding of Kilauea's flank offscraped these deposits to
build an extensive frontal bench. A broad basin formed behind the bench
and above the embayed flank. Uplift and back tilting of young basin fill
indicate recent, and possibly ongoing, bench growth. The Hilina slump
now impinges upon the frontal bench; this buttress may tend to reduce
the likelihood of future catastrophic detachment